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# M1 Momentum question jan 2007

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1. Hey.
How can i conclude on part ii (a) that the direction of motion of n is reversed.
I calculated the total momentum after as being positive but i don`t see how this helps.
Thanks
2. (Original post by SamuelN98)
...
The total momentum in the direction of M is positive, yes. If N were to continue in the original direction then both spheres/particles would have a negative momentum. So it must be the case than N reverses its direction.
3. (Original post by Zacken)
The total momentum in the direction of M is positive, yes. If N were to continue in the original direction then both spheres/particles would have a negative momentum. So it must be the case than N reverses its direction.
So after the collision M is travelling in the opposite direction?
4. (Original post by SamuelN98)
So after the collision M is travelling in the opposite direction?
Okay, so M is travelling to the right and N is travelling to the left. Their combined momentum before colliding is 0.85 (+ve) in the direction of M's motion (so total momentum before collision positive towards the right).

Then M collides with N, the total momentum after is also positive (momentum is conserved) towards the right. But if N was travelling to the left (i.e original path, then so should M because well, imagine it, N is pushing M) so the momentium would be negative in the direction to the right. But we know the momentum is positive, so N must be moving right i.e: opposite. We don't know about M.

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